This invention relates to a method and apparatus for removing contaminants such as oil from metal scrap, and more particularly, for removing a processing oil from aluminum scrap either in briquet, loose form, etc.
In all industries today, the reprocessing of scrap is becoming more and more attractive from an economical standpoint, and this is primarily true because of the scarcity of the natural resources. In the metal industries, and in particular the aluminum industry, one of the major problems with regard to reprocessing scrap aluminum is the processing oil that remains on the scrap metal after it has been worked. Large amounts of sheet and foil scrap are generated in the production of sheets and light gauge foil products. Generally these scraps are contaminated with oil and additives having a wide boiling point range of between about 150.degree. F. to 1100.degree. F.
There are usually two basic types of oily scrap generated by rolling processes: (1) trim scrap; and (2) machine scrap. The trim scrap is produced when trimming the edges of the sheets during the rolling and coiling process or during the slitting process. Machine scrap is cut from the coils and consists of out-of-gauge materials, tails, rejected materials and returned goods. Scrap may also be generated due to unusable products such as wire, cable, automobile parts and machine shop turnings, etc. and can be of any shape or form. The scrap is usually briquetted for convenience of handling and storage with the trim scrap and machine scrap briquets having a density of approximately 30% and 40-60%, respectively, of virgin aluminum.
If the oil contaminated briquets are charged into a furnace, the oil catches fire and a black smoke is generated during the melting process. The fire generated by the burning oil increases the surface temperature of the briquets and creates additional oxides which result in dross and melt loss. The increased dross results in melt loss not only due to the formation of oxides but because pure metal is trapped in the dross. The amount of dross varies but, in an average melting operation, is approximately 20% recoverable aluminum by weight; therefore, the removal of the oil from scrap is most important because melt recovery is improved. An added advantage is that the air quality standards set by the Environmental Protection Agency (EPA) can be met more easily by reducing the amount of smoke generated during melting.